Question

A solution M turns blue litmus red, so it must contain __ ions, another solution O turns red litmus blue and hence, must contain __ ions.

Answer 1

Try to recall the working of a litmus solution under the presence of acid and a base. The ions present in an acid and a base are responsible for the change in colour. Acids turn blue litmus solution red and bases turn red litmus solution blue.

Complete step by step answer:
Litmus is a water-soluble mixture of different dyes extracted from lichens.
-Litmus solution is either extracted on a filter paper or directly used in acid base titrations.
-Litmus solution turns red in the presence of an acid and turns blue in presence of a base.
-Litmus paper is commonly used to detect the strength of ${{H}^{+}}$ ions in a solution i.e. to find the pH (potenz of hydrogen) in a solution.
-Blue litmus solution turns red in the presence of an acid because the pigment reacts with the ${{H}^{+}}$ ions present in the acid to reflect a longer wavelength of light which is red colour.
- Red litmus solution turns blue in the presence of a base because the pigment reacts with the $O{{H}^{-}}$ ions present in the base to reflect a shorter wavelength of light which is blue colour.
From the above explanation we can conclude that solution M turns blue litmus red due to the presence of ${{H}^{+}}$ ions. On the other hand, solution O turns red litmus solution blue due to the presence of $O{{H}^{-}}$ ions.

Note: A litmus solution is made up of several pigments which are acidic or basic in nature. It is the $O{{H}^{-}}$ and ${{H}^{+}}$ that contribute to the chemical reaction for change in colour and not their complementary ions.